The project is called Superboot and the good work is done by paul.
As he describes, Superboot is a boot.img that when flashed, will root your device the first time you boot. the work is done automatically, no need to flash the system partition, no need to use ADB, no overwriting the ROM on your device, just flash the boot image. The instruction are blow:
Download SuperBoot and extract
Step 1. – Switching to Bootloader mode – Turn off the google phone, then press and hold the trackball to enter the bootloader.
Step 2. – On Windows open ‘install-superboot-windows.bat’,
Mac OS X – Open a terminal window to the directory containing the files, and type
chmod +x install-superboot-mac.sh
On Linux – Open a terminal window to the directory containing the files, and type ‘
chmod +x install-superboot-linux.sh